Flat panel displays have recently been developed for visually displaying information generated by computers and other electronic devices. Typically, these displays are lighter and utilize less power than conventional cathode ray tube (CRT) displays. One type of flat panel display is known as a cold cathode field emission display (FED).
A field emission display uses electron emissions to generate a visual image. The field emission display includes a baseplate and a faceplate. The baseplate includes arrays of emitter sites associated with corresponding pixel sites on the faceplate. Each emitter site is typically formed as a sharpened projection, such as a pointed apex or a sharp edged blade. The baseplate is separated from the faceplate by a vacuum gap. A gate electrode structure, or grid, is associated with the emitter sites and functions to provide the intense electric field required for generating electron emission from the emitter sites. When a sufficient voltage differential is established between the emitter sites and grid, a Fowler-Nordheim electron emission is initiated. The emitted electrons strike and excite cathodoluminescent phosphors contained on the face plate. This releases photons thereby providing a light image that can be seen by a viewer. The current flow from the baseplate to the emitter sites is termed the "cathode current" and the electron flow from the emitter sites to the faceplate is termed the "emission current".
The baseplate of a field emission display includes arrays of emitter sites and circuitry for addressing the arrays and activating electron emission from the emitter sites. The baseplate can include a substrate formed of silicon or a hybrid material such as silicon on glass. Different techniques have been developed in the art for addressing the arrays and for activating electron emission from the emitter sites. In addition, a technique must be employed to achieve variations in display brightness when the emitter sites are activated. One such technique is to vary the charge delivered by an emission array in a given frame. Another technique is to vary the emission current produced during activation by varying the cathode current.
One problem with either technique is that the emitter sites of an array can produce significantly different emission currents as a result of small variations in geometry and surface morphology. These variations in emission current tend to degrade the quality of the image. Some of this image variation can be controlled by fabricating emitter sites with a high degree of uniformity and by forming a large number of emitter sites for each pixel site of the display face. Further image improvement can be achieved electrically by operating the emitter sites with a grid capable of producing higher than the desired electron emission current and then limiting or regulating the cathode current supplied to the emitter sites. A wide variety of passive and active current limiting approaches are taught by the prior art.
One such approach is to form electrical resistors in series with the individual emitter sites and arrays of emitter sites. This technique is described in U.S. Pat. No. 3,671,798 to Lees entitled "Method and Apparatus Limiting Field Emission Current". Another example of this approach is described in U.S. Pat. No. 5,283,500 to Kochanski wherein a patterned resistive material is formed in the electrical path to limit cathode current to the emitter sites. One other technique is to deposit a silicon resistive layer on the baseplate subjacent to the emitter sites to limit cathode current to the emitter sites. This technique is described in the 1986 Ph.D. thesis by Dr. Kon Jiun Lee entitled "Current Limiting of Field Emitter Array Cathodes". Another article by Ghis et al published in IEEE , vol 38, no. 10 (October 1991) entitled "Sealed Vacuum Devices Fluorescent Microtip Displays" also discloses series resistors to limit cathode current.
The present invention is directed to improved methods for forming high resistance resistors for limiting cathode current to the emitter sites of a field emission display. Accordingly, it is an object of the present invention to provide improved methods for forming high resistance resistors for regulating cathode current in field emission displays and other flat panel displays.
It is a further object of the present invention to provide improved methods of current regulation for field emission displays using high resistance resistors included in a baseplate of the field emission display.
It is still another object of the present invention to provide improved resistors for field emission displays that are simple, adaptable to large scale manufacture and which can optionally be formed with low resistance ohmic contacts.
Other objects, advantages and capabilities of the present invention will become more apparent as the description proceeds.